The present disclosure relates to a fuel injection controller and a controlling method for an engine.
There is known a fuel injection controller for an engine in which feedback control of a fuel injection amount is performed such that an exhaust air-fuel ratio, which is detected by an air-fuel ratio sensor installed in an exhaust passage, approaches a target air-fuel ratio, and learns as an air-fuel ratio learning value a correction amount of a fuel injection amount required for achieving a target air-fuel ratio based on the result of the feedback control. Further, as seen in Japanese Laid-Open Patent Publication No. 11-287145, there is known an air-fuel ratio controller that maintains an air-fuel ratio of an entire engine provided with a plurality of cylinders at a target air-fuel ratio and corrects fuel injection amounts of the respective cylinders to differentiate air-fuel ratios of air-fuel mixture burned in the cylinders.
When the correction for respective cylinders as described above is in operation, the exhaust air-fuel ratio keeps fluctuating with the target air-fuel ratio at the center. Thus, when air-fuel ratio learning is performed while the correction for respective cylinders is in operation, an air-fuel ratio learning value fluctuates with the exhaust air-fuel ratio. Deterioration in convergence of air-fuel ratio learning values due to the correction for respective cylinders can be prevented by evenly prohibiting or limiting the air-fuel ratio learning when the correction for respective cylinders is in operation. However, this causes a delay in completion of learning of the air-fuel ratio learning value.